E36 M52B28 Misfires once warmed up with decreasing rev range

[zero 1162]

On a friends m52b28 we had a misfire we couldn't figure out. After changing all the plugs and coil packs for new ones as prescribed by the mechanic, the problem was still there.

We got the car scanned again with a different mechanic, and a different scanner, and got way more accurate results.

Turned out that the little shunt resistor in the coil pack harness had become brittle and broken. We just soldered it back together, and problem fixed.

Months and nearly $1000 and still not fixed, and then 30mins with a decent scanner and a soldering iron and problem solved.

Edited December 31, 2015 by zero

[KwS 2425]

it'd be cheaper to chuck the car on a trailer/transporter and send it somewhere reputable like Glenn, than to keep scatter-gunning parts at it with someone who doesnt know what they are doing.

[Bushmechanic 1]

I thought Ron Wood was a reputable place. Now its not?

[Bushmechanic 1]

On a friends m52b28 we had a misfire we couldn't figure out. After changing all the plugs and coil packs for new ones as prescribed by the mechanic, the problem was still there.

We got the car scanned again with a different mechanic, and a different scanner, and got way more accurate results.

Turned out that the little shunt resistor in the coil pack harness had become brittle and broken. We just soldered it back together, and problem fixed.

Months and nearly $1000 and still not fixed, and then 30mins with a decent scanner and a soldering iron and problem solved.

Have you got more info on these resistors? I feel the misfire issue has not been resolved and I have spent money replacing a good camshaft sensor that didn't need doing.

[zero 1162]

The shunt resistor is in the long black plastic box (see pic below) on top of the injectors that houses the coil pack harness. The plastic box just unclips from itself to reveal the wiring and the shunt resistor. The resistor has a small black carbon casing around it that may or may not be intact - they tend to disintegrate over time because of age and the heat of the engine. Break the carbon casing (if any is left) to see if the resistor is still intact. If the resistor is broken just replace or solder it back together. I used heatshrink over the resistor in place of the broken carbon.

The morale of the story though, as has been repeated constantly in this thread, is to get it properly scanned by a bmw specialist (like Glenn) who has the proper scanning gear (like Glenn). Otherwise you are throwing money at guesses, which as you have proven is very expensive, time consuming, and frustrating.

[KwS 2425]

I thought Ron Wood was a reputable place. Now its not?

Im not in Auckland, so i dont know who that is (and the name doesnt sound familiar), but if a workshop takes 2.5 weeks to incorrectly diagnose an issue.... IMO they're looking in the wrong direction.

[Bushmechanic 1]

This is very helpful! I will eventually need to take it to Glenn. At this stage because I have spent the cash with Ron Wood I'll have to take the car back there. Don't get me wrong though, would love to take it to Glenn!

[Bushmechanic 1]

The shunt resistor is in the long black plastic box (see pic below) on top of the injectors that houses the coil pack harness. The plastic box just unclips from itself to reveal the wiring and the shunt resistor. The resistor has a small black carbon casing around it that may or may not be intact - they tend to disintegrate over time because of age and the heat of the engine. Break the carbon casing (if any is left) to see if the resistor is still intact. If the resistor is broken just replace or solder it back together. I used heatshrink over the resistor in place of the broken carbon.

The morale of the story though, as has been repeated constantly in this thread, is to get it properly scanned by a bmw specialist (like Glenn) who has the proper scanning gear (like Glenn). Otherwise you are throwing money at guesses, which as you have proven is very expensive, time consuming, and frustrating.

Thanks heaps zero this is awesome. I will check this out. I'm fairy on to it mechanically so shouldn't be an issue to tackle this. The car spent 2 and a half weeks at Ron Wood auto getting scanned etc. They tried all sorts of fixes and eventually replaced an already replaced camshaft sensor. Although the misfires have decreased its still there andbi van replicate it. The car is now missing at low revs and cuts out. Also has very late starts. So I consider this a step backwards. All the bits i replaced improved the car but did not fix or worsen the misfire issue. I will definitely check out your suggestion on the resistor. The problem originally came on very suddenly. My guess is that something let go and I instantly had a problem.

[zero 1162]

This is very helpful! I will eventually need to take it to Glenn. At this stage because I have spent the cash with Ron Wood I'll have to take the car back there. Don't get me wrong though, would love to take it to Glenn!

#facepalm.

[_ethrty-Andy_ 2132]

I think fuel tank vent is blocked or partially blocked, air not going into the tank fast enough as fuel comes out of it. It's behaving exactly as my V12 E34 did right after build. Something like that wouldn't show up in a scanner

[Bushmechanic 1]

I think fuel tank vent is blocked or partially blocked, air not going into the tank fast enough as fuel comes out of it. It's behaving exactly as my V12 E34 did right after build. Something like that wouldn't show up in a scanner

It happened only when the car was warmed up. What you described would happen at anytime yes?

[Bushmechanic 1]

#facepalm.

They charged me a premium and I need to get my money's worth!

[zero 1162]

They charged me a premium and I need to get my money's worth!

Why pay them more money when they dont know what the problem is?

And how do you know its an electrical problem, and not a fuel or vacuum problem?

[zero 1162]

I think fuel tank vent is blocked or partially blocked, air not going into the tank fast enough as fuel comes out of it. It's behaving exactly as my V12 E34 did right after build. Something like that wouldn't show up in a scanner

Or fuel tank purge valve, although the purge valve should show up on a scan.

[zero 1162]

I have screen shots of all the readings from the scan but dont know how to post here.

If you cant post the picture, then type down what they say on here.

Alos, have you had a compression test done?

[polley 916]

I think fuel tank vent is blocked or partially blocked, air not going into the tank fast enough as fuel comes out of it. It's behaving exactly as my V12 E34 did right after build. Something like that wouldn't show up in a scanner

Easy way to prove if that is the problem or not is to remove the fuel cap and see if the problem goes away.

[tawa 150]

Easy way to prove if that is the problem or not is to remove the fuel cap and see if the problem goes away.

Or as soon as it happens run around and open the tank cap and listen for a whoosh (best done on near empty tank). Semi common problem on bikes with carbs; seen pics of an EFI one that sucked in it's fuel tank though...

[Bushmechanic 1]

Why pay them more money when they dont know what the problem is?

And how do you know its an electrical problem, and not a fuel or vacuum problem?

They gave me the car back telling me the issue is resolved. Its not. But they wouldn't release the car until we paid them. So I've really paid for something that's not fixed and now I have another issue as a result. I'll take it back and see what they say. I understand from checks everything is OK including compression and fuel pump. All hoses have been checked and I understand a smoke test was done to see if there is a vacuum leqk. None found. My scanner kept showing camshaft sensor after I replaced it. So I replaced it again. No change. They have gone and done the same. The only difference is that they pulled out the DME and checked it. Saying it was damp they replaced with a known good item but the problem remained the same. So wasn't the DME.

[polley 916]

If cam and crank signals were out of phase it would consistently throw errors. You could check this with a dual channel scope at the ecu end, this would eliminate any wiring loom issues as well.

Decent live data and a brain could give similar results. Your obviously chasing your tail here and spending a lot of coin at the same time.

[Bushmechanic 1]

If cam and crank signals were out of phase it would consistently throw errors. You could check this with a dual channel scope at the ecu end, this would eliminate any wiring loom issues as well.

Decent live data and a brain could give similar results. Your obviously chasing your tail here and spending a lot of coin at the same time.

Just scanned it on my machine. Gave crankshaft sensor fault 83. I cleared the code and started car again. No fault codes present. I will test drive tomorrow and recheck. Can by the by, crankshaft sensor is new.

[polley 916]

Yeah codes aren't helpful, you need live data.

[zero 1162]

What scanner do you have?

The cheap ones are far from accurate - best to get it scanned on a proper scanner.

I presume the shop has a proper scanner and scanned it - what results did they get on their scanner?

[Bushmechanic 1]

UPDATE:

Issue fixed. New Cam and Crank sensors have been fitted along with temp sensor. no more codes and car runs perfect. outgoing cam and crank sensors have been tested as ok. pretty baffling scenario here. but I'm just glad its all over!

thank you everyone that tried to help. Much appreciated.

I am now in the process of setting up a cold air intake and installing new roof canvas. that's going to be fun!

[zero 1162]

Who fixed the final problems?

Was it that auto electrical place you took it to earlier?

Glad to see its sorted.